Phonograph pickup



June 2, 1953 E, COMBS 2,640,888

PHONOGRAPH PI CKUP Filed Nov. 7, 1949 FIG'S |2| [I22 1 r1 1 m n2 us n4 F'IG.3 FIG.6

INVENT EDWARD E C BS 7 7 Manag n ATTORNEY Patented June 2, 1953 UNITED STATE-S PATENT OFFICE P-HONOGRAPH PICKUP Edward Combs, Albanyfflalif.

Application November ."1, 1949, swarms-26,005

'3 "Claims. '(Cl. fill-400.41)

(Granted under Title 35, U. S. (has (1952'), see. 266) The invention described herein may be manu- :Eactured and used by or for Government tor governmental purposes, without the payment 01 any royalty thereon.

This invention relates to electromagnetic devices and more particularly to phonograph pickups for use with laterally cut disc recordings. This invention is a device for generating voltage in response to and proportional to a mechanical motion such as that of a phonograph needle tracking the groove of a phonograph record.

Certain existing phonograph pic1 -ups of the electromagnetic type are similar in structure to a DArsonval type galvanometer with a phonograph needle in place of the indicating needle. In this type of pick-up, a coil is mounted on jewel, or other precise hearings, to pivot about an axis inthe plane of its windings and perpendi'cular to magnetic lines of force. The phonograph needle is usually rigidly attached to the coil mounting and the coil is free to rotate about the axis in response to tangential mechanical pressure on the needle from the sides of the phonograph record groove. This causes the coil to cut the lines of magnetic force and produce a voltage proportional to the rotational rate of the needle.

The existing electromagnetic pick-dips of this "type usually have the axial pivot mechanism in the plane of and at opposite ends of the coil, with the sections of the coil in quadrature to the pivoted ends of the coil free to cut the ma g netic lines of force. The needle is mounted in the plane of this axis and perpendicular to the magnetic lines of force. A. rigid ferrous section is almost invariably mounted. between the magnetic poles, inside the coil, to provide a low impedance flux path. between the magnetic poles. further concentrating the magnetic lines of force in the area to be traversed by the coils. This axial mounting is subject to friction if not delicately made and subject to damage or displace ment by shock in any of several directions if delicately made.

It is an object of this invention to provide an electromagnetic pick-up wherein the entire center section moves with the coil or" wire.

It is an object of this invention to provide an electrom'agnetic pick-up of the DArsonval type of unusually rugged construction wherein the center section forms a base for the movable coil.

It is an object of this invention to provide a phonograph pick-up of the electromagnetic type whose movable coil is not mounted on small fixed bearings.

It is an object of this invention to provide a phonograph pick -up of the moving coil type whose movable coil. is mounted in a resilient 'bearing material between the coil and magnet.

It is a further object of this invention to provide an electromagnetic coil mounting that will withstand severe shock and that is relatively highly resistant to displacement in any direcnon.

According to iiiy invention the movable member of the lT lCl1*l-.l}3 consists of a cylindrical Torin about which coil is embedded in a continuous groove, in a plane parallel to the axis 'of the cylinder, so that the coil does not project from the body of the cylinder. The needle socket or the pick up is embedded in the cylindrical form in a plane per endicular to the plane of the cell. A ermanent magnet with its pole pieces racing each other and shaped to term 'a cylinder larger 'ilst 'desc forms the lifted cit-lit) 313; that can be c up arm. The mov able cylinder is mounted vi-i him the cylinfliically shaped opening of the pole pieces embedded in a resilient bearing "material so that the movahle cylinder is held free from any contact with the magnetic structure and rotatable about its axis within the limited are required for this purpose.

My invention will be described with reference to the accompanying drawings in which Figs. 1, 2 and 3 represent one species or the invention and i, 5 and 6 represent the second species.

Considering the Pick-up assembly in playing position, Figs. 1 and l show the view from below, Figs. 2 and 5 show one views, and Figs. 3 and 6 are cross sections of the armature forms. Like elements are similarl numbered in all drawings.

Referring now to Fig. 1, the permanent magnot ii) is in the form of a horseshoe with two soft iron pole pieces H and i2 each connected at one end to a pole of the permanent magnet and with the other ends facing each other, without touching, to form a cylindrical section wherein the armature assembly 13 is contained. The spacing between H and i2 is such that the magnetic flux between them is fairly uniformly distributed through the cross section of the air gap. The spacing of the lower part of the gap ii'iust be suiiicient to avoid contact between the pieces I! and I2 and the needle socket M at its maximum deviation.

The armature l3, shown in Fig. 3, fits within the cylindrical section formed by H and I2 with equal spacing all around. The armature of Fig. 3 is cross sectioned to show the coil winding 3 space I 5, the general position of the needle socket I 4 and the position of the threaded hole I5 for the needle set screw ll of Fig. 1 that retains the phonograph needle in its socket, I4.

The coil 23 is wound within the coil winding space and does not project beyond the cylindrical form of the armature I3. The wire may be of any convenient size to give the desired output impedance of the pick-ups. Values from about 1 to about 1000 ohms are readily obtained.

Terminals 20 are attached to the armature to provide suitable contact points between the coil and any external connecting wire or lugs.

The armature is mounted in the cylindrical space, centered and separated from the soft iron pieces I I and I2 by a resilient bearing material I8 that also secures the armature within this space. This material must be resilient enough to not appreciably limit the motion of the armature as the needle follows the record grooves and at the same time the material can have any desired damping eifect. The material may be rubber, synthetic elastomer, or any material resilient enough to meet the above requirements. This type of mounting will withstand shock in any direction and recover itself with relatively little possibility of permanent damage.

Another species of this invention is shown in Figs. 4, 5 and 6. In Fig. 4 the magnet I I0 is attached to ferrous elements I I I and I I2 that form a low reluctance path to direct the magnetic flux to a cylindrical space formed where III and H2 face each other without contacting each other as do elements II and I2 of Figs. 1 and The armature I I3 placed in this space could be identical to the armature l3 and identically mounted, but for this species of applicants invention, an. armature is used as in Fig. 6 with two coils I23A and I23B, wound parallel to the axis of the armature, instead of one. The two coils are equidistant from and symmetric about the axis. They can be connected either in series or parallel to act as a single electrical unit.

The needle set screw may be mounted in the axis of the armature which is also the axis of rotation, The needle set screw mounting [I6 which is correspondingly centered in the armature H3 may be of magnetic material so that the fiux path between poles III and H2 will include the center shaft H6 and will be more or less radial about this shaft. This will result in a highly uniform magnetic field within the limits of the are described by the coils. Thus, the relation between rotation of the coil and the induced currents is correspondingly linear and the harmonic distortion produced is negligible.

This type of construction permits greater mechanical as well. as electrical symmetry than is found in existing electromagnetic pick-ups of this type.

The needle socket H4 in this armature can be made to extend through the armature with a projection I22 of the general shape and mass of the needle, ositioned symmetrically to the needle at the opposit side of the armature. This further dynamically balances the armature. The phonograph needle may be of such conventional shape as N9 of Fig. 5.

The projection I22 may fit into a resilient damper I2I attached to the fixed section of the pick-up. This would further limit the lateral motion of the needle and armature assembly to 4 prevent excessive rotation. The characteristic response curve of this pick-up can be to some extent altered and corrected by the choice of resilient material for this damper.

The coil terminals I20 may be mounted in any convenient place on the armature, preferably on the opposit end to the needle set screw. Two terminals are normally required, although three terminals or more could be provided for pushpull operation as well as extra terminals for various impedance outputs.

The armature H3 can be secured in the cylindrical space between poles III and H2 in the same manner as armature I3 is mounted between poles II and I2. In this case, the resilient hearing II8 may be similar to I8 of Figs. 1 and 2. However, the bands I I8 A and B shown in Fig. 4, would afford greater relative resiliency while giving substantially the same support as I8 and using less material.

The foregoing disclosure illustrates the main feature of my invention. Other variations embodying standard physical and electrical details are considered within the scope of this invention.

I claim:

1. A phonograph pick-up device for use with laterally cut disc recordings, comprising: magnet means having two opposing pole pieces, each of which is adapted to receive a cylindrical ele ment; a cylindrical non-magnetic armature positioned between said pole pieces, said armature having at least one coil thereupon Wound parallel to its axis and being adapted to receive a phonograph needle projectin at right angles to said axis; cylindrical resilient bearing means coaxial with and entirely encasing said armature, said bearing means being disposed within said pole pieces and serving to support said armature as Well as confine its motion to the arc of a circle and a projection of substantially the same size, shape and mass as said phonograph needle symmetrically positioned on the opposite side of said armature from said needle.

2. The device of claim 1, wherein resilient means is positioned between said pole pieces and receptive of said projection to act as a damper to motion of said armature.

3. The device of claim 1, wherein said armature has a ferrous cylindrical member positioned coaxially therein and adapted to receive means for holding said needle in position within said armature.

EDWARD E. COMBS.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,781,376 Eisenhaur Nov. 11, 1930 1,835,073 McClatchie Dec. 8, 1931 1,981,793 Keller Nov. 20. 1934 2,148,796 Barbieri Feb. 28, 1939 2,290,057 Lindenberg July 14, 1942 2,479,894 Andrews Aug. 23, 1949 2,483,196 Gordon Sept. 27, 1949 FOREIGN PATENTS Number Country Date 333,922 Italy Jan. 16, 1936 627,983 Germany Mar. 26, 1936 725.264 France Feb. 11. 1932 

